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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>F.45. test_decoding — SQL-based test/example module for WAL logical decoding</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="tcn.html" title="F.44. tcn — a trigger function to notify listeners of changes to table content" /><link rel="next" href="tsm-system-rows.html" title="F.46. tsm_system_rows — the SYSTEM_ROWS sampling method for TABLESAMPLE" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.45. test_decoding — SQL-based test/example module for WAL logical decoding</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="tcn.html" title="F.44. tcn — a trigger function to notify listeners of changes to table content">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules and Extensions</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="tsm-system-rows.html" title="F.46. tsm_system_rows — the SYSTEM_ROWS sampling method for TABLESAMPLE">Next</a></td></tr></table><hr /></div><div class="sect1" id="TEST-DECODING"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.45. test_decoding — SQL-based test/example module for WAL logical decoding <a href="#TEST-DECODING" class="id_link">#</a></h2></div></div></div><a id="id-1.11.7.55.2" class="indexterm"></a><p>
<code class="filename">test_decoding</code> is an example of a logical decoding
output plugin. It doesn't do anything especially useful, but can serve as
a starting point for developing your own output plugin.
</p><p>
<code class="filename">test_decoding</code> receives WAL through the logical decoding
mechanism and decodes it into text representations of the operations
performed.
</p><p>
Typical output from this plugin, used over the SQL logical decoding
interface, might be:
</p><pre class="programlisting">
postgres=# SELECT * FROM pg_logical_slot_get_changes('test_slot', NULL, NULL, 'include-xids', '0');
lsn | xid | data
-----------+-----+--------------------------------------------------
0/16D30F8 | 691 | BEGIN
0/16D32A0 | 691 | table public.data: INSERT: id[int4]:2 data[text]:'arg'
0/16D32A0 | 691 | table public.data: INSERT: id[int4]:3 data[text]:'demo'
0/16D32A0 | 691 | COMMIT
0/16D32D8 | 692 | BEGIN
0/16D3398 | 692 | table public.data: DELETE: id[int4]:2
0/16D3398 | 692 | table public.data: DELETE: id[int4]:3
0/16D3398 | 692 | COMMIT
(8 rows)
</pre><p>
</p><p>
We can also get the changes of the in-progress transaction, and the typical
output might be:
</p><pre class="programlisting">
postgres[33712]=#* SELECT * FROM pg_logical_slot_get_changes('test_slot', NULL, NULL, 'stream-changes', '1');
lsn | xid | data
-----------+-----+--------------------------------------------------
0/16B21F8 | 503 | opening a streamed block for transaction TXN 503
0/16B21F8 | 503 | streaming change for TXN 503
0/16B2300 | 503 | streaming change for TXN 503
0/16B2408 | 503 | streaming change for TXN 503
0/16BEBA0 | 503 | closing a streamed block for transaction TXN 503
0/16B21F8 | 503 | opening a streamed block for transaction TXN 503
0/16BECA8 | 503 | streaming change for TXN 503
0/16BEDB0 | 503 | streaming change for TXN 503
0/16BEEB8 | 503 | streaming change for TXN 503
0/16BEBA0 | 503 | closing a streamed block for transaction TXN 503
(10 rows)
</pre><p>
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="tcn.html" title="F.44. tcn — a trigger function to notify listeners of changes to table content">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="tsm-system-rows.html" title="F.46. tsm_system_rows — the SYSTEM_ROWS sampling method for TABLESAMPLE">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.44. tcn — a trigger function to notify listeners of changes to table content </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> F.46. tsm_system_rows —
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